The invention relates to a lateral shifting system for floor transport vehicles, especially for fork lift trucks, which have a lift carriage with a basic frame having an upper and lower rail for mounting the fork tines, while on the upper rail, secured against transverse shifting, there is placed a first hooked frame member to which a hydraulic jack is attached and on which a lateral shifting frame can be turned back on its upper horizontal frame member against the direction of travel and can be shifted by the hydraulic drive across the direction of travel, and wherein a lower horizontal frame member of the lateral shifting frame can be joined to the lower rail so as to be displaceable across the direction of travel.
Such lateral shifting frames serve to compensate moving or positioning errors on the part of the driver of the floor transport vehicle in picking up and/or letting down a load, by means of the transverse displacement of a load pickup device which hereinbelow shall be referred to as fork tines considered as being representative also of types of load pickup devices other than forks. The transverse motion can amount to about 15 to 20 centimeters on either side of a central position, although this dimension is not critical. Without an adjuster the driver error would have to be compensated by repetitively moving the vehicle backward and forward.
The lateral shifting systems are therefore inserted between the base frame of a lift carriage on the side of the truck and the fork tines and for this purpose they have a lateral shift frame whose upper and lower edges coincide in position with those of the base frame, so that the fork tines can be placed either on the base frame of the lift carriage or on the lateral shift frame. The geometrical form and the spacing of the edges are standard, as a rule.
Such lateral shifters are disclosed by DE 27 16 668 C2 and the applicant's brochure "Freisicht-Seitenschieber T 151 P2 and T 151 P3" available since 1994.
The base frame, sometimes referred to as the base plate, has upper and lower horizontal frame members whose vertical dimensions amount as a rule to a multiple of their thickness. Strengthening is provided by vertical frame members and by fastening to the lift carriage. As shown in DE 27 16 668 C2, the cross section of at least the lower horizontal frame member of the lateral shift frame is at least similar to the horizontal frame member of the base frame. Thus the lateral shift flame, which is subject to flexure and twist, is heavy, and the known horizontal frame members also hamper the driver's view, inasmuch as in the known systems the hydraulic actuator necessary for transverse movement additionally obstructs the driver's view. A view of the load being carried, however, is essential to the driver for reasons of safety as well.
It is also apparent from the commercial brochure referred to above that the upper and lower horizontal frame members of the lateral shift frame are at least geometrically similar to those of the base frame. The upper horizontal frame member is bolted to two separate and vertically spaced hydraulic jacks whose confronting plungers act upon an abutment fixedly disposed on the base frame, so that the lateral shift frame is displaceable crosswise together with the hydraulic jacks. This known solution is also difficult to manufacture and it is very heavy in weight, which is undesirable inasmuch as the shifter frame increases the so-called "front-end bulk" and, due to its weight, places an additional load on the front axle of the vehicle. Moreover, in this solution the driver's view is restricted.
GB 2 099 787 A, U.S. Pat. No. 5,368,435 and FR 24 37 374 U have disclosed placing on the base frame of a lift carriage first a mounting frame member with a cylindrical outer surface, and then an upper horizontal frame member of a lateral shift frame, provided with a cylindrical inside surface, the cylindrical surfaces forming a joint and a displacement track. Various means are provided to block any upswing of the lateral shift frame. In all cases the hydraulic actuators are articulately connected and have also only one piston rod.
The apparatus according to GB 2099787 A has on the lower horizontal frame member two hooks which can rotate on blocks and which have to be secured by pins after they are turned to the locking position. Both of the horizontal frame members have massive cross sections, and the cylindrical inside surface of the upper horizontal frame member is part of a channel frame member which is welded on. Manufacture is complex and the weight is great.
In U.S. Pat. No. 5,368,435 only the upper horizontal frame member is made in a weight-saving manner, and the lock against upswing is provided by hooks which are vertically adjustable between L-shaped projections and can be locked down by set screws. This increases the distance between the base frame and the lateral shift frame. This patent also discloses slide blocks of plastic, but they are held by the L-shaped projections and an additional angle frame member and therefore cannot be inserted from the side. Mounting and dismounting are accordingly difficult.
In FR 2 437 374 U the two horizontal frame members of the lateral shift frame have equally massive cross sections similar to those of the base frame. The lock against upswing of the lateral shift frame consists of two L-shaped angles, each with a claw screwed to it. This also undesirably increases the distance between the two frames and thus the lever arm. Moreover, the view through the two frames is greatly restricted.
GB 2 007 186 A and DE 23 39 431 A1 do not disclose any definite pivot for the placement of the lateral shift frame on the basic frame of the lift carriage.
The apparatus of GB 2 007 186 A has an additional frame intermediate between the base frame and the lateral shift frame, which bears a hydraulic actuator. Thus, the distance between the base frame and the lateral shift frame becomes especially great. Furthermore, two projecting L-shaped guide rails are mounted on the intermediate frame, and the lateral shift frame has two additional projecting L-shaped guide rails in an arrangement complementary thereto. Two hooks serve to secure against upswing of the intermediate frame from the base frame, the guides of which run through the entire height of the intermediate frame and have to be locked by pins. The lateral shift frame anyway can be pushed onto the intermediate frame only from the side, which is difficult on account of the tendency to tip over. This arrangement has an especially unfavorable weight, and the driver's view is almost completely blocked.
Although DE 23 39 431 A1 discloses a lateral shift frame with two horizontal frame members, the latter do have a small cross sectional area in the shape of an "h" and a low weight, and this lowers resistance to flexure, which is a disadvantage in the rough usage which floor transport vehicles experience. The lateral shift frame can be mounted on the base frame only from the side. The vertical frame members of the lateral shift frame are behind the base frame, so that either their length of movement is limited or the distance between the frame members of the base frame has to be too great. Furthermore, the driver's view is substantially obstructed.